Apparatus for Generating Fluorine Gas

ABSTRACT

[Object] To provide a fluorine gas generating system which can stably supply high purity fluorine gas while preventing blockade of a purification apparatus for adsorbing and removing hydrogen fluoride. 
     [Solving means] A fluorine gas generating system characterized by including a purification apparatus  20  for adsorbing and removing hydrogen fluoride vaporized from a molten salt of an electrolysis tank  1  and mixed in fluorine gas generated at an anode  7,  in which the purification apparatus  20  includes a cylindrical member through which main-product gas containing fluorine gas generated in the electrolysis tank  1  flows, a temperature regulator for regulating temperature of the cylindrical member, and an adsorbent holder disposed inside the cylindrical member, the adsorbent holder being disposed to form an aperture for securing a flow passage of the main-product gas inside the cylindrical member.

TECHNICAL FIELD

This invention relates to a fluorine gas generating system forgenerating fluorine gas.

BACKGROUND TECHNIQUE

Hitherto the following fluorine gas generating system has been known:The fluorine gas generating system includes an electrolysis tank inwhich hydrogen fluoride is electrolyzed in an electrolysis bathincluding a molten salt containing hydrogen fluoride so that amain-product gas whose main component is fluorine gas is generated at ananode side while a by-product gas whose main component is hydrogen gasis generated at a cathode side.

In the fluorine gas generating system of this kind, hydrogen fluoridegas vaporized from the molten salt is mixed in fluorine gas generated atthe anode of the electrolysis tank. Therefore, in order to separatehydrogen fluoride gas from gas generated at the anode so as to purifyfluorine gas, a purification apparatus having a treatment cylinderfilled with adsorbent such as sodium fluoride (Nan or the like isprovided.

Fluorine and hydrogen gases generated from the electrolysis tank containhydrogen fluoride vaporized from the molten salt contained in theelectrolysis tank and mist components of the molten salt itself. Thesecomponents cause deterioration of the adsorbent. Particularly withhydrogen fluoride having a high concentration, the adsorbent near atreatment cylinder inlet may make its expansion or fusion, therebyresulting in clogging of the adsorbent. When such clogging arises, flowof gas is suppressed thereby causing a blockade, which is problematic.

As a technique for solving this problem, Patent Citation 1 disclosessuch a technique that a separating means is provided to form a spacebetween a gas introduction opening and adsorbent in a purificationapparatus filled with the adsorbent such as sodium fluoride (NaF) or thelike, in which liquid drops of the mist components are released andsettled within this space, thus forming a configuration in which theadsorbent and the liquid drops of the mist components are hard tocontact with each other, thereby suppressing clogging of the adsorbentand reducing the frequency of maintenance of the purification apparatus.

PRIOR ART CITATIONS Patent Citation

Patent Citation 1: Japanese Patent Provisional Publication No.2009-215588

SUMMARY OF THE INVENTION Problems to be Solved by Invention

However, in case that the fluorine gas generating system is operated fora long time or in case that the flow rate of generated gas is large, theamount of hydrogen fluoride gas and mist components contacting with theadsorbent increases with the prolonged operation time of the system orthe increased amount of the gas and mist components. Therefore, in aconfiguration using the purification apparatus which is compactly filledwith the adsorbent as described in Patent Citation 1, if clogging of theadsorbent once arises, flow path for gas cannot be secured so as toblock the purification apparatus, thus interrupting a continuousoperation of the fluorine gas generating system, which is problematic.

Thus, it is difficult to completely prevent blockade inside thepurification apparatus with a configuration of being compactly filledwith adsorbent for adsorbing hydrogen fluoride in a purificationapparatus for adsorbing and removing hydrogen fluoride contained influorine gas and hydrogen gas generated in an electrolysis tank of aconventional fluorine gas generating system.

The present invention has been made in view of the above problems andhas an object to provide a fluorine gas generating system which canstably supply high purity fluorine gas while preventing blockade of apurification apparatus for adsorbing and removing hydrogen fluoride.

The present inventors have made eager studies in order to solve theabove-discussed problems. As a result, they have found to be able tostably supply high purity fluorine gas while preventing blockade withina purification apparatus by providing an adsorbent holder inside acylindrical member disposed in the purification apparatus for adsorbingand removing hydrogen fluoride and allowing gas generated in anelectrolysis tank to flow therethrough, and further by disposing thisadsorbent holder in such a manner as to form an aperture for securing agas flow passage for gas flowing through the inside of the cylindricalmember, in an inside space of the cylindrical member, and reached thepresent invention.

That is, the present invention is a fluorine gas generating system forgenerating fluorine gas by electrolyzing hydrogen fluoride in a moltensalt containing hydrogen fluoride, characterized by comprising: anelectrolysis tank in which hydrogen fluoride is electrolyzed in anelectrolysis bath including the molten salt containing hydrogen fluorideto generate a main-product gas whose main component is fluorine gas atan anode side and a by-product gas whose main component is hydrogen gasat a cathode side; and a purification apparatus in which hydrogenfluoride mixed in the main-product gas is removed by an adsorbent,wherein the purification apparatus includes a cylindrical member throughwhich the main-product gas passes, a temperature regulator forregulating a temperature of the cylindrical member, and an adsorbentholder disposed inside the cylindrical member, the adsorbent holderbeing disposed to form an aperture for securing a flow passage of themain-product gas inside the cylindrical member.

Additionally, the present invention is a fluorine gas generating systemcharacterized in that the adsorbent holder includes plural or moreadsorbent holders disposed to meander the flow passage of themain-product gas.

Additionally, the present invention is a fluorine gas generating systemcharacterized in that the adsorbent holder is a tray-like member, thetray-like member including a bottom plate section formed with a cutoutsection for allowing gas to flow therethrough, an outer periphery sidewall section disposed standing at outer periphery of the bottom platesection except for the cutout section, and a cutout side wall sectiondisposed standing at a cutout section side of the bottom plate section,and an upper end opening section of a main body of the tray-like member,and in that the outer periphery side wall section is disposed tointernally contact with inner wall of the cylindrical member.

Additionally, the present invention is a fluorine gas generating systemcharacterized in that the bottom plate section is formed with athrough-hole.

Additionally, the present invention is a fluorine gas generating systemcharacterized in that the adsorbent holder includes plural or moreadsorbent holders disposed separate from each other in the cylindricalmember, wherein a distance between the tray-like member and the adjacenttray-like member is not less than ⅕ of inner diameter of the cylindricalmember and less than the inner diameter of the cylindrical member.

Additionally, the present invention is a fluorine gas generating systemcharacterized in that an area of the bottom plate section formed withthe cutout section is not less than 50% and not more than 95% of an areaof an inner diameter section of the cylindrical member.

Effects of the Invention

According to the present invention, an aperture which is not filled withthe adsorbent is formed inside the cylindrical member disposed in thepurification apparatus and allowing gas generated in the electrolysistank to flow therethrough, so as to provide a configuration for alwayssecuring a gas flow passage. Accordingly, the present invention canprovide a fluorine gas generating system which can stably supply highpurity fluorine gas without causing blockade even in case that a part ofthe adsorbent makes its clogging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fluorine gas generating systemaccording to an embodiment of the present invention;

FIG. 2 is a diagrammatic illustration of a purification apparatusaccording to the embodiment of the present invention;

FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 2;

FIG. 4 is a view showing an example of a tray-like member according tothe embodiment of the present invention; and

FIG. 5 is a diagrammatic illustration of an experimental apparatus withwhich a purification performance test of a purification apparatusapplicable to the embodiment of the present invention was carried out.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be discussedwith reference to drawings. A fluorine gas generating system 100according to the embodiment of the present invention will be discussedwith reference to FIG. 1.

The fluorine gas generating system 100 is configured to generatefluorine gas by electrolysis and supply the generated fluorine gas to anoutside apparatus 4. The outside apparatus 4 is, for example, asemiconductor production equipment, in which fluorine gas is used, forexample, as cleaning gas in a production process for semiconductor.

The fluorine gas generating system 100 includes an electrolysis tank 1for generating fluorine gas under electrolysis, a fluorine gas supplysystem 2 for supplying the outside apparatus 4 with fluorine gasgenerated from the electrolysis tank 1, and a by-product gas treatingsystem 3 for treating by-product gas generated with generation offluorine gas.

First, the electrolysis tank 1 will be discussed. A molten saltcontaining hydrogen fluoride (HF) is stored in the electrolysis tank 1.In this embodiment, a mixture of hydrogen fluoride and potassiumfluoride (KF) is used as the molten salt.

The inside of the electrolysis tank 1 is divided into an anode chamber11 and a cathode chamber 12 by a dividing wall 6 dipped in the moltensalt. An anode 7 and a cathode 8 are dipped respectively in the moltensalt of the anode chamber 11 and the molten salt of the cathode chamber12. By supplying electric current to between the anode 7 and the cathode8 from an electric power source 9, a main-product gas whose maincomponent is fluorine gas (F₂) is generated at the anode 7 while aby-product gas whose main component is hydrogen gas (H₂) is generated atthe cathode 8. A carbon electrode is used as the anode 7 while softmetal, Monel or nickel is used as the cathode 8.

A first gas chamber 11 a to which fluorine gas generated at the anode 7is introduced and a second gas chamber 12 a to which hydrogen gasgenerated at the cathode 8 is introduced are divided on the liquidsurface of the molten salt in the electrolysis tank 1 in such a mannerthat each gas is prevented from transferring between the gas chamber 11a and the gas chamber 12 a. Thus, the first gas chamber 11 a and thesecond gas chamber 12 are completely separated from each other by thedividing wall 6 in order to prevent fluorine gas and hydrogen gas fromreacting with each other under mixing and contacting with each other. Incontrast, the molten salt in the anode chamber 11 and the molten salt inthe cathode chamber 12 are not separated from each other by the dividingwall 6 so as to be communicated with each other through the lower sideof the dividing wall 6.

Since the melting point of KF•2HF is 71.7° C., the temperature of themolten salt is adjusted at 91 to 93° C. Hydrogen fluoride vaporizes fromthe molten salt by an amount corresponding to a vapor pressure and mixedinto each of fluorine gas and hydrogen gas which are respectivelygenerated at the anode 7 and the cathode 8 of the electrolysis tank 1.Thus, fluorine gas is contained in each of fluorine gas generated at theanode 7 and introduced into the first gas chamber 11 a and hydrogen gasgenerated at the cathode 8 and introduced into the second gas chamber 12a.

Next, the fluorine gas supply system 2 will be discussed. A first mainpassage 15 is connected to the first gas chamber 11 a to supply fluorinegas to the outside apparatus 4.

A first pump 17 is disposed in the first main passage 15 to introducefluorine gas outside the first chamber 11 a and convey fluorine gas. Adisplacement pump such as a bellows pump, a diaphragm pump or the likeis used as the first pump 17. A purification apparatus 20 is disposed ina part of the first main passage 15 upstream of the first pump 17 totrap hydrogen fluoride mixed in fluorine gas so as to purify fluorinegas. The purification apparatus 20 will be discussed in detail after.

Next, the by-product gas treatment system 3 will be discussed. A secondmain passage 30 is connected to the second gas chamber 12 a to dischargehydrogen gas to outside.

A second pump 31 is disposed in the second main passage 30 to introducehydrogen gas outside the second gas chamber 12 a and convey hydrogengas. A de-toxifying section 34 is disposed in a part of the second mainpassage 30 downstream of the second pump 31 so that hydrogen gasconveyed by the second pump 31 is made harmless by the de-toxifyingsection 34 and released.

The fluorine gas generating system 100 includes a raw material supplysystem 5 to supply and supplement hydrogen fluoride as a raw material offluorine gas into the molten salt in the electrolysis tank 1.Hereinafter, the raw material supply system 5 will be discussed.

The electrolysis tank 1 is connected through a raw material supplypassage 41 to a hydrogen fluoride supply source for storing hydrogenfluoride to be supplemented to the electrolysis tank 1. Hydrogenfluoride stored in the hydrogen fluoride supply source 40 is suppliedinto the molten salt in the electrolysis tank 1 through the raw materialsupply passage 41.

Additionally, a carrier gas supply passage 46 is connected to the rawmaterial supply passage 41 to introduce a carrier gas supplied from acarrier gas supply source 45 into the raw material supply passage 41.The carrier gas is a gas for introduce hydrogen fluoride into the moltensalt, in which nitrogen gas which is an inert gas is used as the carriergas. Nitrogen gas is supplied into the molten salt in the cathodechamber 12 and discharged from the second gas chamber 12 a through thesecond main passage 30, in which nitrogen hardly dissolves in the moltensalt.

Next, the purification apparatus 20 will be discussed. The purificationapparatus 20 is an apparatus for allowing hydrogen fluoride mixed influorine gas to be adsorbed to an adsorbent such as sodium fluoride(NaF) or the like thereby to remove hydrogen fluoride mixed in fluorinegas.

An inlet line 51 a for introducing fluorine gas generated at the anode 7and an outlet line 52 a for introducing fluorine gas outside thepurification apparatus 20 are connected to the purification apparatus20. Additionally, the purification apparatus 20 includes a cylindricalmember 31 a through which fluorine gas passes, and an adsorbent holderis disposed inside the cylindrical member 31 a to hold the adsorbent foradsorbing hydrogen fluoride.

The cylindrical member referred to here represents a container foraccommodating thereinside the adsorbent for adsorbing hydrogen fluoride,for allowing fluorine gas generated from the electrolysis tank 1 to passtherethrough and for adsorbing and removing hydrogen fluoride influorine gas, in which the shape of the cylindrical member is notparticularly limited. The material of the cylindrical member ispreferably one having a resistance characteristics to fluorine gas andhydrogen fluoride gas, for example, alloy or metal such as stainlesssteel, Monel, nickel or the like.

Many porous beads formed of sodium fluoride (NaF) are used as theadsorbent. The adsorbing ability of sodium fluoride changes according totemperature, and therefore a heater 41 a is disposed around thecylindrical member 31 a so as to serve as a temperature regulator forregulating the temperature inside the cylindrical member 31 a.

The temperature regulator is not particularly limited as far as it canregulate the temperature inside the cylindrical member. For example, aheating or cooling device using a heater, steam heating, heating mediumor cooling medium may be used.

Chemical to be used as the adsorbent is preferably alkali metal fluoridesuch as NaF, KF, RbF, CsF or the like, in which NaF is particularlypreferable.

The adsorbent holder is disposed to form an aperture for securing a gasflow passage inside the cylindrical member 31 a. By this, even in casethat a part of the adsorbent makes its clogging, blockade does not occurstructurally thereby allowing gas to flow.

The adsorbent holder referred to here represents one which is disposedinside the cylindrical member of the purification apparatus andaccommodates and hold a certain amount of the adsorbent in a spaceinside the cylindrical member. Additionally, a plurality of theadsorbent holders may be disposed at regular intervals.

Further, in order to increase the rate of surface area of the adsorbentcontacting with gas flowing inside the cylindrical member, it ispreferable that the adsorbent holder is formed with through-hole(s). Thethrough-holes referred to here are not particularly limited and suitablydesigned as far as they have such sizes as to allow gas to passtherethrough. Additionally, the adsorbent holder is preferably porous ormesh-like, taking account of the rate of surface area of the adsorbentcontacting with gas.

The specific shape of the adsorbent holder is not particularly limitedas far as the adsorbent holder can secure the gas flow passage insidethe cylindrical member and accommodate and hold the adsorbent. Examplesof the specific shape are, for example, a mode in which the adsorbent isfilled in a cylindrical basket-shaped member formed of wire netting(mesh-shaped), a mode in which the adsorbent is filled in a tray-likemember such as a tray-like container, a mode in which the adsorbent isinterposed between sheet-like metals (including mesh-shaped ones), andthe like.

The method of disposing the adsorbent holder in the cylindrical memberof the purification apparatus is not particularly limited as far as theadsorbent holder is disposed to form the aperture for securing a gasflow passage inside the cylindrical member. Examples of the method are,for example, a method for hanging the adsorbent holder of theabove-discussed modes within the space inside the cylindrical member, amethod for disposing the adsorbent holder to be fixed to the inner wallof the cylindrical member, and the like.

Thus, by using the adsorbent holder to be disposed to form the aperturefor securing a gas flow passage inside the cylindrical member, even incase that a part of the adsorbent makes its clogging, the gas flowpassage can be always secured inside the cylindrical member, therebypreventing blockade and making it possible to effectively carry outpurification of gas.

The adsorbent holder is particularly preferably the tray-like membertaking account of practical treatments such as workability duringformation of through-holes in the adsorbent holder, disposing theadsorbent holder to the cylindrical member, easiness of filling theadsorbent to the adsorbent holder, and the like. The tray-like memberreferred to here represents a flat container for accommodating thereinan object. The shape of the tray-like member is not particularly limitedto a generally circular shape, a generally rectangular shape or thelike, and therefore suitably designed according to the shape of thecylindrical member.

Hereinafter, the tray-like member is given as a preferable example ofthe adsorbent holder, and the purification apparatus 20 in which thetray-like member is disposed will be discussed with reference to FIG. 2.It is to be noted that explanation will be made upon using the tray-likemember as an example of the adsorbent holder; however, the adsorbentholder in the present invention is not limited to the tray-like member.

Additionally, FIG. 3 shows a A-A cross-sectional view of thepurification apparatus 20. Additionally, FIG. 4 is a view showing anexample of the structure of the tray-like member to be used as theadsorbent holder.

First, the outline of the purification apparatus 20 in which thetray-like member is disposed will be discussed with reference to FIGS. 2and 3. As shown in FIGS. 2 and 3, a part of the tray-like member 211 isfixed to the inner wall of the cylindrical member 31 a disposed in thepurification apparatus 20. Additionally, a part of the tray-like member211 is formed with a cutout section 212 through which gas is allowed toflow. By forming this cutout section 212, gas can always flow therebyproviding a structure in which complete blockade cannot occur. It is tobe noted that the adsorbent 70 is filled in the tray-like member 211.

The position of the tray-like member 211 fixed to the inner wall of thecylindrical member 31 a is not particularly limited as far as flow ofgas can be secured, in which it is preferable to allow gas and theadsorbent to sufficiently contact with each other thereby to improve apurification efficiency of gas. For example, as shown in FIG. 2, two ormore tray-like members 211 are preferably alternately disposed to theinner wall of the cylindrical member 31 a in such a manner that thecutout sections 212 are located alternately left and right in a flowdirection of from the inlet of gas to the outlet of the gas in thecylindrical member 31 a. By taking such a configuration, the flow of gasis meandered, so that the distance of from the inlet of gas to the flowpassage of the outlet of gas can be increased inside the cylindricalmember 31 a, thereby making it possible to largely improve apurification efficiency of gas.

Additionally, in case that the two or more tray-like members aredisposed separate from each other, it is preferable that the distance ofthe tray-like member 211 and the tray-like member located adjacent theformer tray-like member is ⅕ or more of the inner diameter of thecylindrical member 31 a and not more than the inner diameter of thecylindrical member. If this distance is less than ⅕, gas may not flowsmoothly. If this distance is more than the inner diameter, the flow ofgas cannot be sufficiently meandered so that gas cannot be sufficientlyallowed to contact with the adsorbent.

The number (number of stages) of the tray-like members 211 is preferablyplural (see Example 1 discussed after) in order to completely preventblockade of the purification apparatus and to improve an adsorbingability of hydrogen fluoride; however, the number is preferably suitablyset according to the amount of hydrogen fluoride to be adsorbed, thecondition of the purification apparatus to be used such as the size ofthe apparatus and the like.

Additionally, the size and the arrangement condition of the tray-likemember 211 are not particularly limited as far as the flow of gas is notprevented, and therefore preferably suitably set according to theconditions such as the size and the like of the cylindrical member inwhich the tray-like member is disposed.

Next, an example of the structure of the tray-like member in the presentinvention will be discussed in detail with reference to FIG. 4.

As shown in FIG. 4, the tray-like member 211 of the present inventionincludes a bottom plate section 211 a formed with the cutout section 212for allowing gas to flow, an outer periphery side wall section 211 bwhich is formed standing along the outer periphery of the bottom platesection 211 a except for the cutout portion 211, a cutout side wallsection 211 c which is formed standing at the side of the cutout sectionof the bottom plate section 211 a, and an upper end opening section 211d of the main body of the tray-like member 211.

Additionally, as shown in FIG. 3, it is preferable that the tray-likemember 211 is disposed in such a manner that the outer periphery sidewall section 211 b of the tray-like member 211 except for the cutoutsection 212 is internally in contact with the inner wall of thecylindrical member 31 a. With such a configuration, the amount of theadsorbent 70 to be filled can be increased, and gas and the adsorbentcan be sufficiently contacted with each other, so that the purificationefficiency of gas can be further improved.

The position of the tray-like member 211 formed with the cutout section212, to be disposed in the space inside the cylindrical member 31 a isnot particularly limited as far as the tray-like member has a shape forsecuring flow of gas, and therefore is suitably designed. For example,in order that a sufficient amount of the adsorbent 70 to be filled isaccommodated and that gas is allowed to sufficiently efficiently flow,the area of the bottom wall section 211 a formed with the cutout section212 is not less than 50%, preferably 50 to 95% and more preferably 85 to95% of the area of the inner diameter section (cross-sectional area on aplane including the inner diameter) of the cylindrical member 31 a. Ifit is less than 50%, a sufficient amount of the adsorbent 70 cannot beaccommodated while flow of gas cannot be meandered, so that gas cannotbe sufficiently brought into contact with the adsorbent. In contrast, ifit is more than 95%, a pressure loss become large so that gas cannotsmoothly flow, which is not desirable.

Additionally, the method of arranging and fixing the tray-like member211 in the space inside the cylindrical member 31 a′ is not particularlylimited as far as flow of gas can be secured, in which the pluraltray-like members 211 are arranged to contact with each other orarranged to separate from each other. For example, in such cases thatthe plural tray-like members 211 are arranged and fixed upon beingcontacted with each other and being laid one upon another in such amanner that the cutout sections 212 are located alternately left andright, the cutout side wall section 211 c may be smaller in height thanthe outer periphery side wall section 211 b so that a flow passage ofgas can be secured under the action of an aperture formed by this heightdifference. With such a configuration, since it is sufficient to lay thetray-like members 211 one upon another, there is such an advantage thata trouble for separately fixing the tray-like member 211 to the innerwall of the cylindrical member 31 a is omitted.

Additionally, in order to increase the surface area of the adsorbent tobe contacted with gas and to improve the efficiency of adsorption,through-holes may be suitably formed in members for constituting thetray-like member 211. The through-hole may be formed in all the membersfor constituting the tray-like member 211. In order to increase thesurface area of the adsorbent to be contacted with gas, it is preferableto form the through-holes particularly in the bottom plate section 211 aor the cutout side wall section 211 c, in which it is preferable to takea configuration in which the through-holes are formed, for example, inthe bottom plate section 211 a and/or the cutout side wall section. Withsuch a configuration, gas and the adsorbent can be sufficientlycontacted with each other thereby further improving the purificationefficiency of gas.

The method for forming the through-holes in the tray-like member 211 isnot particularly limited, in which punching is, for example, given.Additionally, porous or mesh-like members may be used as the tray-likemember formed with the through-holes. Particularly in order to increasethe surface area between gas and the adsorbent, it is particularlypreferable that the bottom plate section 211 a is formed mesh-shaped(see Example 1 discussed after).

It is to be noted that, in case that the bottom plate section 211 a isformed mesh-shaped, complete blockade can be prevented because a gasflow passage is secured in the cutout section 212 even if cloggingoccurs in a mesh-shaped part.

The material for constituting the tray-like member 211 is preferably onewhich is resistant to fluorine gas and hydrogen fluoride, for example,alloy and metal such as stainless steel, Monel, nickel and the like aregiven. Additionally, the same materials as the above-mentioned arepreferably used even in case that the tray-like member is formed porousor mesh-shaped.

Next, flow of gas during operation of the fluorine gas generating system100 of this embodiment will be discussed mainly on operation of thepurification apparatus 20.

Fluorine gas generated at the anode 7 of the electrolysis tank 1 isintroduced through the first main passage 15 to the purificationapparatus 20, and then passes through the inlet valve 13 a in an openedstate and introduced from the inlet passage 51 a provided to thecylindrical member 31 a of the purification apparatus 20 to the insideof the cylindrical member 31 a. At this time, the temperature inside thecylindrical member 31 a is regulated by a heater 41 a disposed aroundthe cylindrical member 31 a. The temperature inside the cylindricalmember 31 a is preferably suitably set according to a desired purity(the concentration of hydrogen fluoride in fluorine gas) of fluorine, inwhich it is preferable to set the temperature inside the cylindricalmember 31 a within a range of from 70 to 100° C. in order to control theconcentration of hydrogen fluoride in fluorine gas introduced from theelectrolysis tank 1 at a value of less than 1000 ppm.

Then, fluorine gas passes through the inside of the cylindrical member31 a provided with the adsorbent holder, in which fluorine gas isbrought into contact with the adsorbent accommodated and held by theadsorbent holder provided inside the cylindrical member 31 a whilefluorine gas is adsorbed. At this time, fluorine gas passes through theaperture inside the cylindrical member, and then gas passed through theinside of the cylindrical member 31 a is discharged through the outletpassage 52 a to the outside of the purification apparatus 20 so as to beintroduced into the outside apparatus 4 such as the semiconductorproducing apparatus.

While generation of fluorine gas generated at the anode 7 of theelectrolysis tank 1 has been discussed above, it is possible to purifyhydrogen gas generated at the cathode 8 of the electrolysis tank 1 byusing a purification apparatus having a similar configuration andcarrying out similar operations.

Additionally, concerning the flow direction of gas passing through thepurification apparatus 20, while a case in which the direction of gasflowing through the purification apparatus is from the lower section tothe upper section has been shown in FIGS. 1 and 2 in the aboveembodiment, the flow direction of gas passing through the purificationapparatus is not particularly limited so that gas may be flown from thelower section to the upper section of the cylindrical member or from theupper section to the lower section of the cylindrical member.

With the above embodiment, effects discussed below can be obtained.

According to the embodiment of the present invention, the aperture whichis filled with no adsorbent is formed inside the cylindrical memberthrough which gas generated in the electrolysis tank provided to thepurification apparatus, thereby taking a configuration in which a gasflow passage can be always secured. Accordingly, even in case that apart of the adsorbent makes its clogging, no blockade occur, thusproviding the fluorine gas generating system which can stably supplyhigh purity fluorine gas.

Further, according to the embodiment of the present invention, even incase that a part of the adsorbent makes its clogging, the remaining partof the adsorbent which is filled in the purification apparatus and hasnot yet made its clogging can be effectively utilized because a gas flowpassage is always secured, thereby making it possible to effectively usethe adsorbent.

It will be apparent that the present invention is not limited to theabove embodiment, and that various changes and modifications may be madein the invention without departing from the spirit and scope thereof.

For example, two or more purification apparatuses may be disposed, inwhich they are used upon being switched from one to another.Additionally, the purification apparatus may be disposed at the side ofthe cathode for generating hydrogen gas, or the purification apparatusesmay be disposed respectively at the side of the anode for generatingfluorine gas and at the side of the cathode for generating hydrogen gas.

Industrial Usability

The present invention can be applied to a system for generating fluorinegas and reduce the load of maintenance operations for recovering andreplacing adsorbent for adsorbing and removing hydrogen fluoride.

Embodiment

A purification performance test for a purification apparatus applicableto the embodiment of the present invention was conducted by using anapparatus as shown in FIG. 5. For the purification performance test,measurement of a differential pressure between an inlet A and an outletB of the purification apparatus which was repeatedly used, andmeasurement of the concentration of hydrogen fluoride in gas at theoutlet were carried out. Hereafter, the purification apparatus using atray-type container as the tray-like member which is an example of theadsorbent holder is referred to as a tray-type purification apparatusand will be discussed.

Specifically, an adsorption step at which hydrogen fluoride is adsorbedin the adsorbent and a desorption step for desorption of hydrogenfluoride are repeatedly made, in which the differential pressure betweenthe gas inlet A and the gas outlet B of the purification apparatus andthe hydrogen fluoride concentration at the gas outlet B were measured ateach of repeated cycles each of which includes the adsorption anddesorption steps, measured results being shown in Table 1. It is to benoted that a case using a vertical filled purification apparatus in thesame experimental conditions is shown as a comparative example. Thevertical filled purification apparatus referred to here represents onein which the adsorbent was compactly filled as it is, inside thecylindrical member provided in the purification apparatus.

EXAMPLE 1

A generally circular tray-type container (formed of stainless steel andhaving an outer diameter of 80 mm) shown in FIG. 4 was used as thetray-like member, and a cutout section was formed at a part of thetray-type container in such a manner that the area of the bottom platesection of the tray-type container is 90% of the area of the innerdiameter section of the cylindrical member. Additionally, the tray-typecontainer was machined to remove the bottom plate section to form anopening, upon which a mesh-shaped metal sheet was inserted into theopening, so that the container used was the tray-type container having abottom plate section formed with through-holes (mesh-shaped) and acutout side wall section formed with through-holes (mesh-shaped). It isto be noted that the material of the tray-type container used wasstainless steel, and the cylindrical member used was cylindrical (havingan inner diameter of 80 mm), the material of the cylindrical memberbeing stainless steel.

As shown in FIG. 5, the tray-type containers of eight stages weredisposed in such a manner that the positions of the cutout sections werelocated alternately left and right in the direction of from the inlet tooutlet for gas and in such a manner as to be generally perpendicular tothe inner wall of the cylindrical member, so that the flow of gas wasmeandered. Each tray-type container was disposed in such a manner thatwhole the outer periphery side wall section except for the cutoutsection was internally contacted with the inner wall of the cylindricalmember. 80 g of sodium fluoride was filled as the adsorbent in eachtray-type container (totally 640 g for the eight stages). Additionally,the temperature inside the cylindrical member was adjusted at 100° C. bya heater disposed on the outer periphery of the cylindrical member.

9% hydrogen fluoride gas diluted with nitrogen gas was flown as a samplegas through the purification apparatus at a flow velocity of 0.7 cm/sec.for 15 hours, in which the differential pressure between the gas inlet Aand the gas outlet B of the purification apparatus was measured by apressure gauge. Additionally, the hydrogen fluoride concentration at thegas outlet B after 15 hours gas flowing was analyzed by FourierTransform Infrared Spectroscopy (FT-IR).

Next, the temperature inside the cylindrical member was adjusted at 250°C. by the heater disposed around the outer periphery of the cylindricalmember, and nitrogen gas was flown through the purification apparatus ata flow velocity of 2.1 cm/sec. thereby accomplishing a desorptionoperation for hydrogen fluoride adsorbed to the adsorbent (sodiumfluoride).

Further, the same adsorption step at which hydrogen fluoride is adsorbedto the adsorbent and the same desorption step for hydrogen fluoride werecarried out by 15 times, in which measurements of the differentialpressure and the hydrogen fluoride concentration were made at each of 15times. As shown in Table 1, even in case that the above steps wererepeatedly carried out by 15 times, a large differential pressure wasnot developed between the gas inlet A and the gas outlet B of thepurification apparatus in the tray-type purification apparatus.Additionally, the hydrogen fluoride concentration at the gas outlet Bwas not more than 1000 ppm at each of 15 times.

From these results, it will be understood that hydrogen fluoride can beeffectively removed preventing blockade in the purification apparatus byusing the tray-type purification apparatus.

COMPARATIVE EXAMPLE 1

A purification performance test was carried out in the same conditionsas those in Example 1 with the exception that the vertical filledpurification apparatus (640 g of sodium fluoride as the adsorbent wascompactly filled as it is).

As a result, in the vertical filled purification apparatus, the hydrogenfluoride concentration at the gas outlet B was not more than 1000 ppm ateach of 15 times; however, the differential pressure became not lowerthan 10000 Pa so that complete blockade was made at the sixth time inthe repeated times.

From [Example 1] and [Comparative Example 1], it is apparent that thetray-type purification apparatus has an equal purification performanceto that of the vertical filled purification apparatus, and is hard tocause blockade.

TABLE 1 Developed differential pressure [Pa] (after flowing for 15hours) Using times 1 2 3 4 5 10 15 Comparative Vertical 133 399 665 26604389 — — Example 1 type Example 1 Tray-type 2 5 3 4 0 5 4

EXPLANATION OF REFERENCE NUMERALS

100 fluorine gas generating system

1 electrolysis tank

2 fluorine gas supply system

3 by-product gas supply system

4 outside apparatus

5 raw material supply system

7 anode

8 cathode

11 a first gas chamber

12 a second gas chamber

15 first main passage

17 first pump

31 second pump

20 purification apparatus

211 tray-like member

211 a bottom plate section

211 b outer periphery side wall section

211 c cutout side wall section

211 d upper end opening section

212 cutout section

1. A fluorine gas generating system for generating fluorine gas byelectrolyzing hydrogen fluoride in a molten salt containing hydrogenfluoride, characterized by comprising: an electrolysis tank in whichhydrogen fluoride is electrolyzed in an electrolysis bath including themolten salt containing hydrogen fluoride to generate a main-product gaswhose main component is fluorine gas at an anode side and a by-productgas whose main component is hydrogen gas at a cathode side; and apurification apparatus in which hydrogen fluoride mixed in themain-product gas is removed by an adsorbent, wherein the purificationapparatus includes a cylindrical member through which the main-productgas passes, a temperature regulator for regulating a temperature of thecylindrical member, and an adsorbent holder disposed inside thecylindrical member, the adsorbent holder being disposed to form anaperture for securing a flow passage of the main-product gas inside thecylindrical member.
 2. A fluorine gas generating system as claimed inclaim 1, characterized in that the adsorbent holder includes plural ormore adsorbent holders disposed to meander the flow passage of themain-product gas.
 3. A fluorine gas generating system as claimed inclaim 1, characterized in that the adsorbent holder is a tray-likemember, the tray-like member including a bottom plate section formedwith a cutout section for allowing gas to flow therethrough, an outerperiphery side wall section disposed standing at outer periphery of thebottom plate section except for the cutout section, and a cutout sidewall section disposed standing at a cutout section side of the bottomplate section, and an upper end opening section of a main body of thetray-like member, and in that the outer periphery side wall section isdisposed to internally contact with inner wall of the cylindricalmember.
 4. A fluorine gas generating system as claimed in claim 3,characterized in that the bottom plate section is formed with athrough-hole.
 5. A fluorine gas generating system as claimed in claim 3,characterized in that the adsorbent holder includes plural or moreadsorbent holders disposed separate from each other in the cylindricalmember, wherein a distance between the tray-like member and the adjacenttray-like member is not less than ⅕ of inner diameter of the cylindricalmember and less than the inner diameter of the cylindrical member.
 6. Afluorine gas generating system as claimed in claim 3, characterized inthat an area of the bottom plate section formed with the cutout sectionis not less than 50% and not more than 95% of an area of an innerdiameter section of the cylindrical member.